Integration of the human immunodeficiency virus type-1 (HIV-1) linear DNA genome into the host chromosome is essential for virus replication. The concerted insertion of the two viral DNA termini into the host genome (full-site reaction) requires the viral integrase (IN). Nonionic detergent lysates of viable HIV-1 virions can readily perform the in vivo full-site reaction using retrovirus-like donor substrates (469 bp) and circular DNA as target. Recombinant IN, purified from bacteria, can perform Only the half-site strand transfer reaction (insertion of only one viral terminus per target molecule). What properties associated with HIV-1 virions allow native IN to catalyze the full-site reaction? We will investigate the molecular mechanisms involved in how HIV-1 IN in virions and purified core particles, or IN purified from virions, can catalyze the 3' cleavage and concerted integration reactions. We will determine if other viral or cellular proteins associated with purified virions act as potential cofactors, either as enhancers or inhibitors, in the assembly and catalysis of preintegration complexes capable of full-site reactions. Efforts will be extended to determine whether an oligomeric structure of dimeric IN is responsible for catalyzing the concerted reaction. We will determine what role the viral terminal sequences have in the assembly of preintegration complexes, using native HIV-1 IN, that prompt the concerted reaction. Using DNA sequence analysis of donor-target recombinants which are genetically selected, we will investigate how native IN prompts the formation of full-site recombinants. We will investigate how an unknown recombinant structurally related to full-site recombinants and how specific sets of host site deletion (17-47 bp) recombinants, having a periodicity of approximately 10 bp between sets, are produced. Using electron microscopy, we will determine if native HIV-1 IN is capable of looping DNA which may play a role in forming and maintaining the 80S nucleoprotein complexes in vivo. Our studies may provide an understanding of the molecular mechanisms involved in the in vivo integration reaction and provide information for the design of IN inhibitors. Combinational inhibitor therapies against the rapid replication of HlV-1 in humans may be necessary to prevent AIDS.